1. Field of the Invention
The present invention relates to apparatus, methodology, systems, and/or computer program product for resolving multiple master conflict in a directory database (DDB) and, more particularly, relates to resolving multiple master conflict in a globally-distributed DDB within a computer network environment such as a client server network.
2. Description of Prior Art
As may be observed by even the most casual computer system user, computer networks appear to be continuously evolving into ever-more sophisticated communication systems. Accordingly, computer networks are having an ever-increasing impact on modern-day lifestyle for many people, as the Internet is demonstrating. Computer networks include local area networks (LANs) such as might be encountered within a singular and localized corporate business organization where corporate functions (engineering, marketing, sales, advertising, human resources, etc.) are linked together in a localized computer network. Computer networks also include wide area networks (WANs) such as might be encountered within a corporate business organization that is nationwide or even worldwide in scope. The Internet is the premier example of a WAN, but is one that is obviously not constrained within any particular business organization and allows access to virtually any organization or individual. It is widely understood that these networks not only utilize hard-wire bus communication paths to accomplish their objectives, but can also utilize wireless telecommunication links via satellites and the like as well.
Computer network configurations usable within LANs and WANs include client-server network configurations. A client or workstation (typically having a user interface) can be networked to multiple servers which serve the client in a variety of ways. Such a client-server computer network configuration can be particularly useful in certain applications, such as in managing a computer data storage system. A client-server network can be used with the Internet. Thus, quality of operation of a storage system within a client-server network operatively coupled over the Internet not only can impact quality of performance of that client-server computer network, but can also impact quality of service received by multiple human users connected through the Internet to that client-server network. A failed or degraded storage system thus can escalate into a failed or degraded service for multiple human users.
A client-server network today may typically be based on an object oriented computer system which means that such system employs one or more object-oriented computer languages such as C++, XML (eXtensible Markup Language), JAVA, and/or others. Briefly, an object, in computer software terms, also referred to as a “node”, is a dedicated area of memory which can be thought of as an impervious container holding both data and instructions within itself, both defining itself and its relationships to other objects in the computer system or network. Such object or node can send and receive messages to and from other objects, respond and react to such messages (e.g. commands) but shall normally be impervious to internal scrutiny. For example, in the above-noted computer data storage system (a kind of computer) each object (system object) may describe or relate to a specific tangible detail in the storage system or in the storage system's processor (e.g., details such as those describing or relating to aspects of operation of the processor's cooling-fan, power switch, cache memory, power supply, disk drive interface, etc.). These tangible objects (nodes) in the storage system can send messages to each other within the storage system and to other objects outside the storage system over the network with which they are operatively coupled. Also, the storage system itself can be an object and interact as a node with other nodes in a network.
The relationship between and amongst these specific objects in the storage system is usually visualized or characterized as a “tree” of objects. In a tree, each such object hangs off a preceding object as if in a parent-child or inheritance relationship, with many children hanging from a parent not being an atypical configuration. In addition to these tangible kinds of objects, logical units (LUNs) are other nodes or objects that can be contained within the tree. For example, a storage system object can have several LUN objects as its children which, in turn, can have various disk objects as their children, etc. These kinds of objects are generically referred to herein as “system objects” since they all relate to a system or to components within a system, whether it is a storage system, computer system, disk drive system, or some other system, and representations of these objects can typically be displayed on a computer terminal's graphical user interface (GUI) in this tree fashion. However, in contrast, other kinds of objects (nodes) can also be formulated which do not relate to a system or its components per se, such as objects relating to user actions and represented on the GUI in other ways. (User actions are any commands or operations initiated by the user, such as, for example, creating a LUN or downloading new software to a disk, etc.). In addition, there can be yet other kinds of network nodes beyond the two types mentioned such as nodes comprising or represented by a communication tree.
Accordingly, it shall be appreciated that there can be a very large number of nodes of various kinds or “personalities” to keep track of and manage within even a relatively small and local computer network. Any one or more of these nodes can fail, for one reason or another, either temporarily or permanently, and certain other nodes can be added or removed by network users under certain conditions, and this complex and dynamic network node scenario must be efficiently and effectively managed if the computer network's intended purpose is to be fulfilled. Moreover, this network node management problem is compounded when the network is large, and possibly worldwide. The subject of these computer network nodes is discussed further in two patent applications filed by the assignee of the present invention: “Plug and Play Interface for User Actions”, Desai et al, U.S. Ser. No. 09/916,102, filed Jul. 26, 2001 and “Scalable Communication Within a Distributed System Using Dynamic Communication Trees”, Bauer et al, U.S. Ser. No. 09/877,862, filed Jun. 8, 2001, both of which are incorporated by reference herein in their respective entireties.
One prior art solution to the problem of managing network nodes is to elect one node to have complete information about all other network nodes in the system. Similarly, a group of nodes can be elected where each elected node in the group is assigned to its own subnet or domain of nodes and has complete information about all other nodes in its own subnet or domain. A subnet or domain is a network unto itself. All other nodes in that network, or in that subnet as the case may be, then seek information necessary to their functioning from their respective one elected node and are thus managed through that one elected node. The inherent weakness in this configuration is that if such one elected node fails, then no other node in its respective network or subnet can function resulting in a failed network or subnet. This is a single point of failure design which is not an optimum design because of at least this problem.
Prior art attempts to make this single point of failure design more reliable included use of backup nodes, to take over functioning of an elected node if and when the elected node failed. The problem with this backup design is that backup nodes can also fail and then the result is the same as before—a failed network or subnet within the network. Furthermore, when dealing with a worldwide network, which is not atypical today, if backup nodes are being relied upon because of potential elected node failures, and if all backup nodes are being maintained in one locale (e.g. United States of America) for convenience, security, or other purposes, then virtually all network node information can be destroyed for that global network if a disaster at the backup locale destroys the backup nodes. This would be a major disruption. All worldwide users (Europeans, Asians, etc.) of that worldwide network would thus lose the service provided by that network.
Effective solutions to these single point of failure problems of the aforementioned prior art are presented in the patent application cross referenced herein, and include use of a master node which can be selected from the ranks of participating nodes in a network domain or configuration. The master node is a privileged node relative to its participating nodes and controls the directory database (DDB) distributed within each of its participating nodes to match its own DDB and thereby be substantially identical from node to node across its domain. The master node is selected or replaced with another node under control of a global administrator, a privileged network user having special password access to enable only him/her to perform these master node changes. It is prudent computer network practice to have only one global administrator per domain, or one person of authority under such global administrator per domain, who selects and changes master nodes.
This master node solution is very satisfactory in any DDB network or domain within that network in which only one master node asserts itself on participating nodes in that network or domain, which may be the usual case, particularly with LANs. However, if another user of the network gains access to the global administrator's password, either with or without proper authorization, and if that other user selects a second master node (a purported or contending master node) in the same domain that had a previously operative master node, then a conflict results. All nodes in the configuration would then be subject to assertions by two different master nodes that each of those master nodes is the true master for each node in that domain. This problem may be compounded further if there are more than only two users having this password access. This problem may be compounded even further if this is a globally-dispersed network where human language barriers can be challenging and result in multiple masters being created by mistake. Further, widely-varying time zone differences (some users are sleeping while others on opposite sides of the globe are working on the global network) might also contribute to multiple masters being created by mistake.
Thus, there is need for a solution to this multiple master conflict problem, and the present invention is an effective solution.